Cat-5 means category 5, and describes a certain kind of twisted pair copper cabling. It is commonly written cat5 or CAT5. Cat5 is the current "standard" for 100 megabit per second network wiring. Depending on implementation it can also serve for both 10Mbps and 1Gbps ("gigabit") ethernet networking connections, 4 or 16Mbps token ring networks, POTS phone cable, ISDN connections, T1 connections, and many others.
The most common use for category 5 cable besides POTS phone networks, or even proprietary phone systems, is for 100Mbps ethernet networks. You can get good transfer rates using 100Mbps ethernet with cat5 over distances as long as 300 meters.
The difference between one category of wire and another is largely defined by the quality of the (copper) wire and the "twist count", the number of times the wire is twisted. Twisted pair wires are twisted in order to reduce electromagnetic interference (EMI) - see twisted pair.
While it doesn't strictly matter which pairs you hook up (as long as you're consistent and you use the wires in pairs) there is a "proper" conventional way to utilize category 5 cable with multiple pairs. The pairs are meant to be used in the following order for POTS service:
The white wire always comes first. You can remember this as "BLOG" BLue, Orange, Green, and brown gets left over. When attaching these to a jack or punchdown block they are always punched down in order. Old cables with green, red, yellow, and black wires should be punched down green/red, and black/yellow, in that order, and would be matched to new wires (if a splice was necessary) in that order.
If your cable has less than five pairs (four pairs is most common for network cabling, as this is what 10base- and 100base-T ethernet networks utilize) then they will appear in their numbered order (I.E. three pair cables have neither brown nor slate wires.) The "white" wire is commonly white with a colored stripe to aid in identifying pairs, though when cutting cable there should never be any exposed wires without the outer jacket. All wires should terminate in junction boxes with a wall plate.
For ethernet, there are two wiring standards: EIA/EIA 568A, and 568B. In both, white wires alternate with colored wires, and the blue pair is always in the center. The white wire comes first, just as for phones. The difference between the two is where the pairs are located. 568A, from pins 1 to 8, runs white/green, green, white/orange, blue, white/blue, orange, white/brown, brown. 568B runs white/orange, orange, white/green, blue, white/blue, green, white/brown, brown. Note that in both types the blue and brown wires do not move, the only difference is the position of green and brown wires. Wiring one end of a cable for 568A and the other for 568B will produce a non-full-duplex crossover cable. For more on ethernet and cat5, see Crimping Cat-5.
Category 5 cable is intended for use with a 100Mhz signal. Using Ethernet this provides a maximum (theoretical) throughput of 100Mbit/s per pair (100Mbps in each direction for full duplex operation.) This cable is intended for use with all types of nbase-T ethernet up to and including 100Base-TX.
The standards for category 5 cable are laid out in ISO/IEC-11801 and TIA/EIA-568-A-5.
- Tech Info - Cable and Wiring FAQ. May 18, 2005 ZyTrax, Inc. (http://www.zytrax.com/tech/layer_1/cables/tech_lan.htm)